diff --git a/src/Form/Field/Checkbox.php b/src/Form/Field/Checkbox.php
index f6358761da..e4d3bb11eb 100644
--- a/src/Form/Field/Checkbox.php
+++ b/src/Form/Field/Checkbox.php
@@ -66,7 +66,7 @@ public function canCheckAll()
      *
      * @return $this
      */
-    public function groups($groups = [])
+    public function groups(array $groups = [])
     {
         $this->groups = $groups;